#9 Rectangulator
Set by Katie Steckles
Given a standard calculator keyboard, press – in order, going either clockwise or anticlockwise – four digit keys that form the corners of a square or rectangle on the keypad. This will create a four-digit number, e.g. 7469.
If the first button you press is the 7 key, how many possible four-digit numbers can you create?
What about if your square or rectangle is allowed to have a height or width of zero?
Can you show that for any square or rectangle you choose, the resulting four-digit number will always be divisible by 11?
Solution next…
